Methods for studying single ionizing particles
Emeléus, Karl George
University of Cambridge
Department of Physics
Doctor of Philosophy (PhD)
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Emeléus, K. G. (1926). Methods for studying single ionizing particles (Doctoral thesis). https://doi.org/10.17863/CAM.11765
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Although it is over a century since the fundamental ideas of the atomicity of matter were first clearly stated by Dalton, yet only within the last two decades has the reality of atoms and sub-atomic particles been established beyond doubt. Final proof of their existence has come with the ability to deal with oertain individual particles, whioh can be recognized by possession of some special property. Of the methods at present available, the most powerful employ the swift particles produced in the process of radioactive disintegration, and amongst these three in particular have been used. The method of scintillations, the oldest, utilizes the fact that an alpha particle or a proton of similar velocity, has sufficiently great energy, coupled with sufficiently small penetrating power to give a visible flash when incident on certain crystals. It is of particular value in that little complication is introduced by the presence of other penetrating radiation, either corpuscular or electromagnetic. The second is based on the property of a swift particle of ionizing a gas through which it is passing, the ions formed being increased in number in an intense eleotrio field till a detectable current has been produced. As will be seen later, it is here very difficult to distinguish between alpha particles and beta particles, and in consequence its applioations are limited. On the other hand, sensitivity to an eleotron permits of the indirect study of individual quanta of radiation by the photo-electric effeot. In the third method, the ionization due to a single particle is again used, but instead of the ions being gathered up, they are now registered as condensation nuclei in a supersaturated vapour, at or very close to their point of origin. The resulting line of dew is a faithful reproduction of the path of the particle. Here again, alpha particles, protons and electrons can all be reoorded, but they are now differentiated by their typical trails. The range of application of these three methods is very wide, but the first two may be grouped together, since what is there directly recorded is the instantaneous presence of a particle at a certain place, its previous history having to be deduced. In the cloud apparatus, on the contrary, we see the aotual path of the particle, and its applications tend to be qualitative rather than quantitative. It will be convenient to divide the work to be described in the following pages into four sections. In the first, the cloud method is applied to study the collisions between alpha particles and electrons (A), and in the second to determine the nature of the path of a fast proton (B). In the third, an acoount is given of the measurement by means of the electrical oounter of a radioactive constant, viz. the beta ray emission from Radium E - (C); and in the last the mechanism of the electrical counter is considered (D). No systematic experiments have. been done involving scintillations .
This record's DOI: https://doi.org/10.17863/CAM.11765